The electrical impedance of an electrical circuit or circuit component is the opposition to current that the circuit or component presents to an applied voltage. Impedance can be a complex quantity, namely the sum of a resistance and a reactance, and can vary with the frequency of the applied voltage. Knowledge of impedance aids in determining the efficiency with which energy is delivered to the load of a circuit. Impedance measurement and analysis can be used in electronic sensors, for example, in determining the properties of a material or workpiece, or conditions of the surrounding environment.
Impedance analyzers can operate by applying a sinusoidal stimulus to the circuit or component under measurement, referred to herein as the “device under test” (DUT), and measuring the electrical response of the DUT to the applied sinusoid waveform. The response may be measured at more than one frequency of the sinusoidal stimulus, for example, over a sweep of input frequencies. The use of a single-frequency sinusoid as the measurement stimulus at each of the frequencies of interest greatly simplifies the measurements, as harmonic interference in the response of the DUT is largely avoided.
Microcontroller-based sensors can be used for the measurement and analysis of electrical impedance. Microcontrollers are large-scale electronic integrated circuits (ICs) that include the computational capability for controlling and managing a wide range of functions and useful applications, including integrating all necessary functional components of a computer system, whether general-purpose or arranged for a particular end application. In some implementations, such microcontrollers are referred to as a “system on a chip” (SoC) device. Some microcontroller architectures include one or more processor cores that carry out the digital computer functions of retrieving executable instructions from memory, performing arithmetic and logical operations on digital data retrieved from memory, and storing the results of those operations in memory. Other digital, analog, mixed-signal, or even RF functions may also be integrated into the same integrated circuit for acquiring and outputting the data processed by the processor cores.